WO2019044331A1 - 加熱条件の設定方法、ファイバブラッググレーティングの製造方法、及びファイバレーザシステムの製造方法 - Google Patents
加熱条件の設定方法、ファイバブラッググレーティングの製造方法、及びファイバレーザシステムの製造方法 Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02171—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for compensating environmentally induced changes
- G02B6/02176—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for compensating environmentally induced changes due to temperature fluctuations
- G02B6/02185—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for compensating environmentally induced changes due to temperature fluctuations based on treating the fibre, e.g. post-manufacture treatment, thermal aging, annealing
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
- G02B6/02204—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using thermal effects, e.g. heating or cooling of a temperature sensitive mounting body
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
- H01S3/0078—Frequency filtering
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
- H01S3/067—Fibre lasers
- H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
- H01S3/2383—Parallel arrangements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S2301/00—Functional characteristics
- H01S2301/03—Suppression of nonlinear conversion, e.g. specific design to suppress for example stimulated brillouin scattering [SBS], mainly in optical fibres in combination with multimode pumping
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/094049—Guiding of the pump light
- H01S3/094053—Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/09408—Pump redundancy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
- H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/16—Solid materials
- H01S3/1601—Solid materials characterised by an active (lasing) ion
- H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
- H01S3/1618—Solid materials characterised by an active (lasing) ion rare earth ytterbium
Definitions
- the present invention relates to a method of setting heating conditions in thermal aging of a fiber Bragg grating.
- the present invention also relates to a method of manufacturing a fiber Bragg grating and a method of manufacturing a fiber laser system.
- Patent Document 1 In order to suppress the temperature rise which may occur at the time of actual use in a fiber bragg grating, there is known a technique for reducing the energy of ultraviolet light irradiated to the fiber bragg grating at the time of manufacture (see Patent Document 1). In addition, in order to suppress a change in reflection characteristics that may occur after shipping in the fiber Bragg grating, a technique is known in which the fiber Bragg grating before shipping is subjected to thermal aging (see Patent Document 2 and Non-Patent Document 1).
- Patent No. 5298238 (Date of registration: June 21, 2013)
- Patent No. 3153083 (Registration date: January 26, 2001)
- Patent Document 1 The technique described in Patent Document 1 is difficult to apply to the production of a high reflection fiber Bragg grating, because it is necessary to reduce the energy of ultraviolet light irradiated to the fiber Bragg grating at the time of production. Therefore, it has been difficult to realize a highly reflective fiber Bragg grating that suppresses the temperature rise that may occur during actual use, using the technique described in Patent Document 1. Further, the technology described in Patent Document 2 enables shipment of a fiber Bragg grating with suppressed change in reflection characteristics that may occur after shipment, and shipment of a fiber Bragg grating with suppressed temperature rise that may occur during actual use. It is not something that makes
- a method of setting a heating condition is a method of setting a heating condition at the time of thermal aging of a fiber Bragg grating, comprising: a temperature coefficient ⁇ of the fiber Bragg grating; and relaxation energy Ed of the fiber Bragg grating Identifying the lower limit value Edmin of the relaxation energy Ed, where the temperature coefficient ⁇ is less than or equal to the desired upper limit value ⁇ max, based on the corresponding relationship ⁇ (Ed) between them, and so that the relaxation energy Ed becomes the lower limit value Edmin or more And setting the heating conditions for thermal aging of the fiber Bragg grating.
- a method of manufacturing a fiber laser system is a pump light source, an amplification fiber, and two fiber Bragg gratings that cause the amplification fiber to function as a resonator, each of which has a reflectance of
- a method of manufacturing a fiber laser system comprising at least one fiber laser unit including two different fiber Bragg gratings, using the method of manufacturing a fiber Bragg grating according to any one of the aspects of the present invention described above And manufacturing each of the two fiber Bragg gratings.
- a method of setting heating conditions when thermally aging a fiber bragg grating the method of setting heating conditions capable of suppressing a temperature rise of the fiber bragg grating which may occur during actual use. be able to.
- FIG. 1 It is a flowchart which shows the flow of the heating condition setting method which concerns on the 1st Embodiment of this invention.
- the application example of the heating condition setting method shown in FIG. 1 is shown.
- (A) is a graph in which values of relaxation energy Ed and temperature coefficient ⁇ are plotted on an Ed- ⁇ plane for a highly reflective fiber Bragg grating having a reflectance of 99.3%.
- (B) is a graph in which values of relaxation energy Ed and temperature coefficient ⁇ are plotted on an Ed- ⁇ plane for a low reflection fiber Bragg grating having a reflectance of 10%.
- (A) is a graph in which time series ICC1 (t), ICC2 (t), and ICC3 (t) are plotted on a t-ICC plane.
- (B) is a graph in which time series NCC1 (t), NCC2 (t), and NCC3 (t) are plotted on a t-NCC plane.
- the application example of the heating condition setting method shown in FIG. 3 is shown. It is the graph which plotted time series (Ed1 (t), NCC 1 (t)), (Ed 2 (t), NCC 2 (t)), and (Ed 3 (t), NCC 3 (t)) on the Ed-NCC plane.
- FIG.1 It is a perspective view which shows the typical example of the fiber Bragg grating which can become application object of the setting method of the heating condition shown in FIG.1 and FIG.3. It is a flowchart which shows the flow of the manufacturing method of the fiber laser system which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the 1st typical example of the fiber laser system which can become application object of the manufacturing method of the fiber laser system shown in FIG. It is a block diagram which shows the structure of the 2nd typical example of the fiber laser system which can become application object of the manufacturing method of the fiber laser system shown in FIG.
- the temperature coefficient ⁇ is defined as the slope d ⁇ / dP when the temperature ⁇ [° C.] of the fiber Bragg grating is regarded as a function ⁇ (P) of the power P [W] of the light guided through the fiber Bragg grating Amount.
- a fiber Bragg grating having a large temperature coefficient ⁇ is likely to become hot in actual use, and has a low long-term reliability.
- a fiber Bragg grating having a small temperature coefficient ⁇ is unlikely to reach a high temperature during actual use, and has a high long-term reliability.
- the correspondence ⁇ (Ed) represented by a specific function exists between the temperature coefficient ⁇ [° C./W] and the relaxation energy Ed [eV].
- the present inventors have found that there is a linear correspondence relationship ⁇ (Ed) represented by a linear function.
- ⁇ is a negative constant
- ⁇ is a positive constant
- the constants ⁇ and ⁇ depend on the structure of the fiber Bragg grating.
- the relaxation energy Ed of the fiber Bragg grating after thermal aging is given by the following equation (2).
- k [eV / K] is a Boltzmann constant
- e is an elementary charge
- ⁇ 0 is a detachment rate
- T is a heating temperature [K]
- t is a heating time [second ].
- the heating temperature T and the heating time t are collectively referred to as heating conditions (T, t).
- the Boltzmann constant k and the elementary charge e are universal constants, and the separation velocity 0 0 is a constant determined in accordance with the structure of the fiber Bragg grating. Therefore, if the heating condition (T, t) for thermal aging is determined, the relaxation energy Ed of the fiber Bragg grating after thermal aging is determined by the above equation (2). Then, if the relaxation energy Ed of the fiber Bragg grating after thermal aging is determined, the temperature coefficient ⁇ of the fiber Bragg grating after thermal aging can be obtained from the above equation (1). Conversely, if the temperature coefficient ⁇ of the fiber Bragg grating after thermal aging is determined, the relaxation energy Ed of the fiber Bragg grating after thermal aging is determined by the equation (1). Then, if the relaxation energy Ed of the fiber Bragg grating after thermal aging is determined, the heating condition (T, t) of thermal aging can be obtained by the above equation (2).
- the heating condition (T, t) of thermal aging can be set so that the temperature coefficient ⁇ of the fiber Bragg grating after thermal aging becomes equal to or less than a desired upper limit value ⁇ max.
- T, t the temperature coefficient of the fiber Bragg grating after thermal aging becomes equal to or less than a desired upper limit value ⁇ max.
- the fiber Bragg grating refers to an optical fiber in which a grating is written in the core.
- FIG. 6 is a perspective view showing a typical fiber Bragg grating 1.
- reference numeral 1 indicates a fiber Bragg grating
- reference numeral 11 indicates a core
- reference numeral 12 indicates a cladding
- Reference numeral 11 a indicates a grating written to the core 11.
- FIG. 1 is a flowchart showing the flow of the heating condition setting method S1.
- the heating condition setting method S1 is a method of setting the heating condition of the thermal aging of the fiber Bragg grating, and includes steps S10 to S12 described below.
- the departure speed ⁇ 0 is known.
- the step S20 included in the heating condition setting method S2 is performed to determine the withdrawal speed 00, which will be described below. Steps S21, S10 to S11, and S22 may be performed.
- Step S10 is a step of deriving a correspondence relationship ⁇ (Ed) between the temperature coefficient ⁇ and the relaxation energy Ed.
- the correspondence relationship ⁇ (Ed) can be expressed by the above equation (1). Therefore, in the present process, the correspondence relationship ⁇ (Ed) is derived by deriving the constants ⁇ and ⁇ included in the above equation (1).
- Derivation of the constants ⁇ and ⁇ in step S10 can be performed, for example, as follows.
- n (where n is a natural number of 2 or more) fiber Bragg gratings, that is, FBG1, FBG2, ..., FBGn are prepared.
- FBG1, FBG2, ..., FBGn are fiber Bragg gratings having the same reflectance.
- Ed1 to Edn are different from each other.
- a specific function representing the correspondence relationship ⁇ (Ed) approximates a set of (Ed1, ⁇ 1), (Ed2, ⁇ 2), ..., (Edn, ⁇ n) with a specific accuracy, Or set the value of the constant included in the function so as to approximate the best.
- the linear function shown in the above equation (1) representing the correspondence relationship ⁇ (Ed) is a set of (Ed1, ⁇ 1), (Ed2, ⁇ 2), ..., (Edn, ⁇ n) with a specific accuracy
- the constants ⁇ and ⁇ included in the equation (1) are set so as to approximate or best approximate.
- the graph of the linear function shown in the above equation (1) is a point (Ed1, ⁇ 1), (Ed2, This can be realized by approximating the set of ⁇ 2),..., (E dn, ⁇ n) with a specific accuracy or searching for values of constants ⁇ and ⁇ that most closely approximate. Alternatively, it can be realized by the method of least squares.
- Step S11 is a lower limit value of relaxation energy Ed, at which temperature coefficient ⁇ is equal to or less than a desired upper limit value ⁇ max, based on the correspondence relationship ⁇ (Ed) between temperature coefficient ⁇ and relaxation energy Ed shown in the above equation (1). It is a process of specifying Edmin.
- the specification of the lower limit Edmin in this step can be performed, for example, as follows. That is, an equation obtained by substituting a desired upper limit value ⁇ max into the equation (1) is solved for Ed, and the solution is set as the lower limit value Edmin.
- the “desired upper limit ⁇ max” refers to, for example, the upper limit ⁇ max arbitrarily determined by the user of the heating condition setting method S1.
- Step S12 is a heating condition such that the relaxation energy Ed is equal to or more than the lower limit value Edmin specified in the step S11, based on the relation between the relaxation energy Ed and the heating temperature T and the heating time t shown in the equation (2).
- This is a step of setting (T, t).
- the setting of the heating conditions (T, t) in this step can be carried out, for example, as follows. That is, the value of the heating temperature T is arbitrarily determined, and the equation obtained by substituting the lower limit Edmin specified in the step S11 into the equation (2) is solved for t, and the solution is defined as the heating time t. Alternatively, the value of the heating time t is arbitrarily determined, the equation obtained by substituting the lower limit Edmin specified in the step S11 into the equation (2) is solved for T, and the solution is taken as the heating temperature T.
- the temperature coefficient ⁇ of the fiber Bragg grating after thermal aging becomes the desired upper limit value ⁇ max or less, that is, the relaxation energy Ed becomes the lower limit value Edmin or more.
- the heating conditions (T, t) of thermal aging can be set.
- the fiber Bragg grating includes a setting step of setting the heating condition (T, t) according to the heating condition setting method S1, and a thermal aging step of thermally aging the fiber Bragg grating according to the set heating condition (T, t). According to the manufacturing method, it is possible to manufacture a fiber Bragg grating in which the temperature rise that may occur in actual use is suppressed.
- said process S10 is a process which arises when the correspondence (gamma) (Ed) between temperature coefficient (gamma) and relaxation energy Ed is unknown, and arises. Therefore, when the correspondence relationship ⁇ (Ed) between the temperature coefficient ⁇ and the relaxation energy Ed is known, the above step S10 can be omitted.
- Table 1 is a table listing heating temperature T, heating time t, relaxation energy Ed, and temperature coefficient ⁇ for a high reflection fiber Bragg grating having a reflectance of 99.3% and a low reflection fiber Bragg grating having a reflectance of 10%. .
- the heating temperature T and the heating time t shown in the first and second rows of Table 1 are the same as those in step S10 (B) in order to obtain a fiber Bragg grating having relaxation energy Ed shown in the third row of Table 1
- the temperature coefficient ⁇ shown in the fourth row of Table 1 is the temperature coefficient ⁇ of the fiber Bragg grating having the relaxation energy Ed shown in the third row of Table 1, and is the value measured in (C) of step S10 above. It is.
- the unit of the heating temperature T is “° C.”, and the unit of the heating time t is “minutes”.
- FIG. 2A is a graph in which the values of relaxation energy Ed and temperature coefficient ⁇ shown in Table 1 are plotted on an Ed- ⁇ plane for a highly reflective fiber Bragg grating having a reflectance of 99.3%.
- FIG. 2A also shows a graph of the linear function ⁇ (Ed) derived in (D) of the above step S10 as a linear function ⁇ (Ed) that best approximates these plots. ing. For example, when the upper limit value ⁇ max of the temperature coefficient ⁇ is 0.2 ° C./W, the lower limit value Edmin of the relaxation energy Ed specified in step S11 is 2.06 eV, as shown in FIG. Can be seen from
- FIG. 2B is a graph in which the values of relaxation energy Ed and temperature coefficient ⁇ shown in Table 1 are plotted on the Ed- ⁇ plane for a low reflection fiber Bragg grating having a reflectance of 10%.
- a graph of the linear function ⁇ (Ed) derived in the above step S10 is also shown as a linear function ⁇ (Ed) that best approximates these plots.
- the upper limit value ⁇ max of the temperature coefficient ⁇ is 0.1 ° C./W
- the lower limit value Edmin of the relaxation energy Ed specified in step S11 is 1.86 eV, as shown in FIG. Can be seen from
- FIG. 3 is a flowchart showing the flow of the heating condition setting method S2.
- the heating condition setting method S2 is obtained by omitting the step S12 and adding the steps S20 to S21 before the step S10 and adding the step S22 after the step S11 in the heating condition setting method S1. Therefore, in heating condition setting method S2, process S20, process S21, process S10, process S11, and process S22 are implemented in this order.
- Step S20 is a step of deriving a correspondence NCC (Ed) between the normalized integrated constant NCC (Normalized Integrated Coupling Constant) and the relaxation energy Ed.
- NCC Normalized Integrated Coupling Constant
- the correspondence relationship NCC (Ed) can be expressed by the following equation (3). Therefore, in this process, constants a, b, c, and v0 included in the following equation (3) are derived. Note that ⁇ 0 is included in Ed according to equation (2).
- Derivation of the constants a, b, c, ⁇ 0 in the step S 20 can be performed, for example, as follows.
- n (where n is a natural number of 2 or more) fiber Bragg gratings, that is, FBG1, FBG2, ..., FBGn are prepared.
- FBG1, FBG2, ..., FBGn are fiber Bragg gratings having the same reflectance.
- the minimum transmission coefficient Tmin refers to the minimum value when the transmission coefficient T is regarded as a function T ( ⁇ ) of the wavelength ⁇ .
- the value NCCi (t) of the normalized coupling constant NCC at each time t of each FBGi is calculated.
- the coupling constant ICC and the normalized coupling constant NCC have the relationship shown in the following equation (5).
- the constants a, b, c and ⁇ 0 included in the above equation (3) are set so as to approximate the set of (t) and NCC n (t) with a particular accuracy or best approximate them. .
- the setting of the constants a, b, c, ⁇ 0 is, for example, a point on the Ed-NCC plane of the graph of the function shown in the above equation (3) while changing the values of the constants a, b, c, ⁇ 0 little by little.
- Step S21 is a relaxation energy in which the normalized coupling constant NCC becomes equal to or less than a desired upper limit NCCmax, based on the correspondence NCC (Ed) between the normalized coupling constant NCC and the relaxation energy Ed shown in the equation (3).
- This is a step of specifying the lower limit Edmin 'of Ed.
- the specification of the lower limit Edmin 'in this step can be performed, for example, as follows. That is, the equation obtained by substituting the desired upper limit value NCCmax into the above equation (3) is solved for Ed, and the solution is taken as the lower limit value Edmin '.
- the “desired upper limit NCCmax” refers to, for example, the upper limit NCCmax arbitrarily determined by the user of the heating condition setting method S2.
- step S22 relaxation energy Ed, heating temperature T, and heating shown in the above equation (2) are used, with Edmax being the larger of the lower limit Edmin specified in step S11 and the lower limit Edmin 'specified in step S21.
- the heating condition (T, t) is set based on the relationship with the time t such that the relaxation energy Ed is equal to or greater than Edmax.
- the setting of the heating conditions (T, t) in this step can be carried out, for example, as follows. That is, the value of the heating temperature T is arbitrarily determined, and the equation obtained by substituting Edmax into the equation (2) is solved for t, and the solution is defined as the heating time t. Alternatively, the value of the heating time t is arbitrarily determined, and the equation obtained by substituting Edmax into the equation (2) is solved for T, and the solution is taken as the heating temperature T.
- the temperature coefficient ⁇ of the fiber Bragg grating after thermal aging becomes the desired upper limit value ⁇ max or less, and the normalized coupling constant NCC of the fiber Bragg grating after thermal aging is
- the heating condition (T, t) of thermal aging can be set so as to be equal to or less than the desired upper limit value NCCmax.
- the fiber Bragg grating includes a setting step of setting the heating condition (T, t) according to the heating condition setting method S2, and a thermal aging step of thermally aging the fiber Bragg grating according to the set heating condition (T, t). According to the manufacturing method, it is possible to manufacture a fiber Bragg grating in which a temperature rise that may occur during actual use is suppressed and a change in reflection characteristics that may occur after shipping is suppressed.
- said process S10 is a process which arises when the correspondence (gamma) (Ed) between temperature coefficient (gamma) and relaxation energy Ed is unknown, and arises. Therefore, when the correspondence relationship ⁇ (Ed) is known, the above-described step S10 can be omitted.
- the above-described step S20 is a step that needs to be performed when the correspondence NCC (Ed) between the normalized coupling constant NCC and the relaxation energy Ed is unknown. Therefore, when the correspondence NCC (Ed) is known, the step S20 can be omitted.
- step S20 is performed prior to step S10. Since step S21 can be performed any time as long as the values of a, b and c are determined in step S20, step S21 may be performed before step S10 or after step S10 and in step S11. It may be carried out before or after step S11.
- step S11 When the value of 0 0 (relaxation constant) is known, the above steps S 10 to S 11 may be performed before the above steps S 20 to 21 may be performed.
- Example of application An application example of the heating condition setting method S2 will be described with reference to FIG. 4, FIG. 5 and Table 2.
- FIG. 4 is a graph in which the time series ICC1 (t), ICC2 (t), and ICC3 (t) obtained in (C) of the above-mentioned step S20 are plotted on the t-NCC plane.
- (B) of FIG. 4 is a graph in which the time series NCC1 (t), NCC2 (t), and NCC3 (t) obtained in (D) of step S20 described above are plotted on the t-ICC plane.
- FIG. 5 shows the time series (Ed1 (t), NCC1 (t)), (Ed2 (t), NCC2 (t)), and (Ed3 (t), (Ed3 (t), It is the graph which plotted NCC3 (t)) in the Ed-NCC plane.
- FIG. 5 also shows a graph of the relationship NCC (Ed) derived in (F) of step S20 described above as the relationship NCC (Ed) that best approximates these plots.
- This relationship NCC (Ed) is obtained by setting the constants a, b, c and ⁇ 0 as shown in Table 2 in the relationship NCC (Ed) defined by the equation (3).
- NCCmax of the normalized coupling constant NCC is 0.8 dB
- Edmin 'of the relaxation energy Ed specified in step S21 is 1.85 eV.
- FIG. 7 is a flowchart showing the flow of the manufacturing method S3.
- FIG. 8 is a block diagram showing a configuration of a fiber laser system FLS which is a first typical example of a fiber laser system to which the manufacturing method S3 can be applied.
- FIG. 9 is a block diagram showing a configuration of a fiber laser system FLS which is a second typical example of a fiber laser system to which the manufacturing method S3 can be applied.
- the fiber laser system FLS of the first typical example is described, and then the manufacturing method S3 of manufacturing the fiber laser system FLS is described. Moreover, after demonstrating fiber laser system FLS, manufacturing method S3 which manufactures fiber laser system FLS is demonstrated.
- the fiber laser system FLS of the first typical example is a laser device for processing the workpiece W to be processed, and as shown in FIG. 8, n fiber laser units FLU1 to FLUn, n laser lasers It comprises delivery fibers LDF1 to LDFn, an output combiner OC, an output delivery fiber ODF, and an output head OH.
- the fiber laser units FLU1 to FLUn and the laser delivery fibers LDF1 to LDFn correspond to each other in a one-to-one relationship.
- n is an arbitrary natural number of 1 or more, and represents the number of fiber laser units FLU1 to FLUn and the number of laser delivery fibers LDF1 to LDFn.
- the output combiner OC also has n input ports and one output port.
- the output combiner OC multiplexes the n laser beams input to each input port into one laser beam, and outputs the multiplexed laser beam from the output port.
- the fiber laser unit FLUi (i is a natural number of 1 or more and n or less) generates laser light.
- forward-pumped fiber lasers are used as the fiber laser units FLU1 to FLUn.
- the fiber laser unit FLUi is connected to the input end of the corresponding laser delivery fiber LDFi.
- the connection point Pib is a point where the output end of the fiber laser unit FLUi (that is, the output end of the amplification fiber AFi) and the input end of the laser delivery fiber LDFi are connected by fusion.
- the laser light generated by the fiber laser unit FLUi is input to the laser delivery fiber LDFi.
- the laser delivery fiber LDFi guides the laser light generated by the corresponding fiber laser unit FLUi.
- the laser delivery fibers LDF1 to LDFn may be single mode fibers or may be fuse mode fibers having a mode number of 10 or less.
- the fuse mode fibers are used as the laser delivery fibers LDF1 to LDFn.
- the output end of the laser delivery fiber LDFi is connected to the input port of the output combiner OC.
- the laser light generated by the fiber laser unit FLUi and guided through the laser delivery fiber LDFi is input to the output combiner OC via the input port.
- the output combiner OC is generated by each of the fiber laser units FLU1 to FLUn, and multiplexes the laser light guided through each of the laser delivery fibers LDF1 to LDFn.
- the output port of the output combiner OC is connected to the input end of the output delivery fiber ODF.
- the laser beams combined by the output combiner OC are input to the output delivery fiber ODF. That is, the incident surface of the output delivery fiber ODF is coupled to the plurality of fiber laser units FLUi via the output combiner OC.
- the output delivery fiber ODF guides the laser light combined in the output combiner OC.
- a multimode fiber is used as the output delivery fiber ODF.
- the output end of the output delivery fiber ODF is connected to the output head OH.
- a space optical system for example, a convex lens, not shown in FIG. 5 for focusing the laser light emitted from the output head OH on the surface of the work W is provided between the output head OH and the work W. ing.
- the laser beam combined by the output combiner OC is emitted from the output head OH, and is irradiated onto the work W in a state of being converged by the space optical system.
- the output combiner OC is employed as an example of the multiplexing unit described in the claims.
- a spatial optical system including a plurality of convex lenses can also be adopted as an example of the multiplexing unit described in the claims.
- this space optical system is configured by n convex lenses, each convex lens focuses the laser light emitted from the laser delivery fiber LDFi of each fiber laser unit FLUi, and outputs each focused laser light It may be arranged to be coupled to the core of the delivery fiber ODF.
- the configuration of the fiber laser unit FLU1 included in the fiber laser system FLS will be described with continued reference to FIG.
- the fiber laser units FLU2 to FLUn are also configured similarly to the fiber laser unit FLU1.
- the fiber laser unit FLU1 is a forward pumping type fiber laser, and as shown in FIG. 8, m pumping light sources PS1 to PSm, m pumping delivery fibers PDF1 to PDFm, pumping combiner PC, high reflection fiber Bragg A grating FBG-HR, an amplification fiber AF, a low reflection fiber Bragg grating FBG-LR, and a slant fiber Bragg grating SFBG are provided. That is, the fiber laser unit FLU1 is a resonator type fiber laser unit.
- the excitation light sources PS1 to PSm and the excitation delivery fibers PDF1 to PDFm correspond one to one with each other.
- m is an arbitrary natural number of 2 or more, and represents the number of excitation light sources PS1 to PSm and the number of excitation delivery fibers PDF1 to PDFm.
- the high reflection fiber Bragg grating FBG-HR is formed in the vicinity of the input end of the amplification fiber AF
- the low reflection fiber Bragg grating FBG-LR is in the vicinity of the output end of the amplification fiber AF.
- the slant fiber Bragg grating SFBG is formed between the low reflection fiber Bragg grating FBG-LR and the output end of the amplification fiber AF.
- the excitation light source PSj (j is a natural number of 1 or more and m or less) generates excitation light.
- laser diodes are used as excitation light sources PS1 to PSm.
- the excitation light source PSj is connected to the input end of the corresponding excitation delivery fiber PDFj.
- the excitation light generated by the excitation light source PSj is input to the excitation delivery fiber PDFi.
- the excitation delivery fiber PDFj guides the excitation light generated by the corresponding excitation light source PSj.
- the output end of the pump delivery fiber PDFj is connected to the input port of the pump combiner PC.
- the pump light generated by the pump light source PSj and guided through the pump delivery fiber PDFj is input to the pump combiner PC via the input port.
- the excitation combiner PC combines the excitation light generated by each of the excitation light sources PS1 to PSm and guided through each of the excitation delivery fibers PDF1 to PDFm.
- the output port of the pump combiner PC is connected to the input end of the amplification fiber AF via the high reflection fiber Bragg grating FBG-HR.
- the connection point Pia is a point at which the output port of the excitation combiner PC and the input end of the amplification fiber AF are connected by fusion.
- the pump light transmitted through the high reflection fiber Bragg grating FBG-HR is input to the amplification fiber AF.
- the amplification fiber AF generates laser light using the excitation light transmitted through the high reflection fiber Bragg grating FBG-HR.
- the excitation light transmitted through the high reflection fiber Bragg grating FBG-HR is used to maintain this rare earth element in a population inversion state.
- the output end of the amplification fiber AF is connected to the input end of the laser delivery fiber LDF1 via a low reflection fiber Bragg grating FBG-LR.
- the high reflection fiber Bragg grating FBG-HR functions as a mirror (reflectance is, for example, 99%) at a certain wavelength ⁇ (for example, 1060 nm), and the low reflection fiber Bragg grating FBG-LR is a half mirror at that wavelength ⁇ It works (the reflectance is 10%, for example). Therefore, the amplification fiber AF, together with the high reflection fiber Bragg grating FBG-HR and the low reflection fiber Bragg grating FBG-LR, constitutes a resonator that oscillates a laser beam of wavelength ⁇ . Among the laser beams generated by the amplification fiber AF, the laser beam transmitted through the low reflection fiber Bragg grating FBG-LR is input to the laser delivery fiber LDF1.
- the slant fiber Bragg grating SFBG gives priority to light belonging to a wavelength band including stimulated Raman scattering light having a wavelength corresponding to the wavelength of laser light generated by the amplification fiber AF over light not belonging to the wavelength band Bond to the cladding.
- the slant fiber Bragg grating SFBG is configured to preferentially lose the stimulated Raman scattering light over the laser light.
- the stimulated Raman scattering light resulting from the laser light generated by the amplification fiber AF transits to the cladding in the process of passing through the slant fiber Bragg grating SFBG.
- the slant fiber Bragg grating SFBG is formed in the subsequent stage of the resonator formed of the high reflection fiber Bragg grating FBG-HR and the low reflection fiber Bragg grating FBG-LR, the induction generated in this resonator Raman scattered light can be removed.
- a cladding mode stripper (not shown in FIG. 8) for leaking the light shifted to the cladding to the outside is provided.
- the stimulated Raman scattering light that has transitioned to the cladding can be quickly leaked to the outside without being fixed to the cladding.
- the slant fiber Bragg grating SFBG and the cladding mode stripper configured as described above function as a filter element for stimulated Raman scattering light.
- forward-pumped fiber lasers are used as the fiber laser units FLU1 to FLUn, but the present invention is not limited to this. That is, in the present invention, backward pumped fiber lasers can be used as the fiber laser units FLU1 to FLUn, and bidirectional pumped fiber lasers can be used as the fiber laser units FLU1 to FLUn.
- the manufacturing method S3 shown in FIG. 7 is a manufacturing method for manufacturing the fiber laser system FLS shown in FIG. 8, and the heating performed between steps S31 to S33 and steps S32 and S33 described below And condition setting method S1.
- heating condition setting method S1 contained in manufacturing method S3 is the same as heating condition setting method S1 shown in FIG. 1, the description is abbreviate
- Step S31 is a step of forming a high reflection fiber Bragg grating FBG-HR and a low reflection fiber Bragg grating FBG-LR in the vicinity of both ends of the amplification fiber AF.
- Step S32 is a step of forming a slant fiber Bragg grating SFBG in the vicinity of one end of the amplification fiber AF. More specifically, among the both ends of the amplification fiber AF, the end on the side on which the low reflection fiber Bragg grating FBG-LR is formed is the output end, and the low reflection fiber Bragg grating FBG-LR and the amplification fiber AF It is a process of forming a slant fiber Bragg grating SFBG between the output end.
- Step S33 thermally ages the high reflection fiber Bragg grating FBG-HR, the low reflection fiber Bragg grating FBG-LR, and the slant fiber Bragg grating SFBG according to the heating condition (T, t) set by the heating condition setting method S1. It is a process.
- the manufacturing method S3 includes a setting step of setting the heating condition (T, t) according to the heating condition setting method S1, and thermal aging for thermally aging the fiber Bragg grating according to the set heating condition (T, t) And a process. Therefore, according to manufacturing method S3, the temperature coefficient ⁇ of each of the high reflection fiber Bragg grating FBG-HR, the low reflection fiber Bragg grating FBG-LR, and the slant fiber Bragg grating SFBG after thermal aging is respectively a desired upper limit
- the heating conditions (T, t) of thermal aging can be set so that the value ⁇ max or less, that is, the relaxation energy Ed becomes the lower limit value Edmin or more. Further, according to the manufacturing method S3, it is possible to manufacture the fiber laser system FLS in which the temperature rise that may occur during actual use is suppressed.
- the heating conditions (T, t) set for each of the high reflection fiber Bragg grating FBG-HR and the low reflection fiber Bragg grating FBG-LR are respectively: Of the fiber Bragg grating after thermal aging is set to a desired upper limit value ⁇ max or less, that is, the relaxation energy Ed is set to a lower limit value Edmin or more. Therefore, the heating conditions (T, t) set for each of the high reflection fiber Bragg grating FBG-HR and the low reflection fiber Bragg grating FBG-LR may be different or the same.
- the low reflection fiber Bragg grating FBG-LR and the slant fiber Bragg grating SFBG are formed close to each other, they are thermally aged according to the same heating condition (T, t). Therefore, it is preferable to set the heating condition (T, t) so as to satisfy the above conditions for both the low reflection fiber Bragg grating FBG-LR and the slant fiber Bragg grating SFBG.
- FIG. A configuration may be adopted in which a grating functioning as a slant fiber Bragg grating SFBG is written in the core of an optical fiber separate from the amplification fiber FA, as in a fiber bragg grating 1C described later.
- the slant fiber Bragg grating SFBG and the cladding mode stripper have been described as being formed between the low reflection fiber Bragg grating FBG-LR and the output end of the amplification fiber AF.
- the slant fiber Bragg grating SFBG and the cladding mode stripper may be formed between the high reflection fiber Bragg grating FBG-HR and the input end of the amplification fiber AF, or the low reflection fiber Bragg grating FBG-LR and It may be formed both to the output end of the amplification fiber AF and between the high reflection fiber Bragg grating FBG-HR and the input end of the amplification fiber AF.
- boron may be added to the amplification fiber AF for the purpose of improving the sensitivity of ultraviolet light.
- the manufacturing method S3 including the heating condition setting method S1 can be suitably used regardless of whether or not boron is added to the amplification fiber AF adopted by the fiber laser system FLS.
- the manufacturing method S3 may be defined so as to include the heating condition setting method S2 shown in FIG. 3 instead of the heating condition setting method S1 shown in FIG.
- the fiber laser system FLS of the second typical example is one in place of the n fiber laser units FLUi included in the fiber laser system FLS (see FIG. 8) of the first typical example.
- the fiber laser unit FLU1 is provided.
- the fiber laser unit FLU1 included in the fiber laser system FLS of the second typical example has the same configuration as the fiber laser unit FLU1 included in the fiber laser system FLS of the first typical example.
- the fiber laser unit FLU1 included in the fiber laser system FLS has a high reflection fiber Bragg grating FBG-HR, a low reflection fiber Bragg grating FBG-LR, and a fiber laser unit FLU1 included in the fiber laser system FLS.
- each of the slant fiber Bragg gratings SFBG is not formed directly on the amplification fiber AF, but is formed on an optical fiber separate from the amplification fiber AF.
- the fiber laser system FLS is a fiber Bragg grating 1A which is an optical fiber in which a grating functioning as a high reflection fiber Bragg grating FBG-HR is written, and a low reflection fiber Bragg grating FBG-LR.
- a fiber Bragg grating 1B which is an optical fiber in which a functional grating is written
- a fiber Bragg grating 1C which is an optical fiber in which a grating that functions as a slant fiber Bragg grating SFBG is written.
- the fiber Bragg gratings 1A and 1B are configured in the same manner as the fiber Bragg grating 1 shown in FIG. 6, and in the fiber Bragg grating 1C, the grating written in the core is inclined with respect to the cross section of the optical fiber It is configured in the same manner as the fiber Bragg grating 1 except that it has.
- the input end of the fiber Bragg grating 1A is connected to the output port of the pump combiner PC at the connection point Pa, and the output end of the fiber Bragg grating 1A is connected to the input end of the amplification fiber AF at the connection point Pb .
- the input end of the fiber Bragg grating 1B is connected to the output end of the amplification fiber at the connection point Pc, and the output end of the fiber Bragg grating 1B is connected to the input end of the fiber Bragg grating 1C at the connection point Pd .
- the incident end of the fiber Bragg grating 1C is connected to the output end of the fiber Bragg grating 1B at the connection point Pd, and the output end of the fiber Bragg grating 1C is connected to the incident end face of the output delivery fiber ODF at the connection point Pe There is.
- the optical fibers are connected by fusion bonding at the connection points Pa, Pb, Pc, Pd, and Pe.
- the fiber laser system FLS shown in FIG. 9 can be manufactured using a modified example in which a part of the manufacturing method S3 shown in FIG. 7 is modified. Here, only the point of changing the manufacturing method S3 shown in FIG. 7 in the manufacturing method S3 of the modification will be described.
- Step S31 included in the manufacturing method S3 of the modified example includes a high reflection fiber Bragg grating FBG-HR and a low reflection fiber Bragg grating FBG-LR in each of the two optical fibers instead of the vicinity of both ends of the amplification fiber AF.
- the optical fiber formed with each of the high reflection fiber Bragg grating FBG-HR and the low reflection fiber Bragg grating FBG-LR is not doped with ytterbium unlike the amplification fiber AF. .
- Step S32 included in the manufacturing method S3 of the modification is a step of forming a slant fiber Bragg grating SFBG in one optical fiber instead of the vicinity of one end of the amplification fiber AF.
- Step S33 included in the manufacturing method S3 of the modification is the same step as step S33 included in the manufacturing method S3 illustrated in FIG. 7.
- the manufacturing method S3 of the modification is a step performed after the step S33, and (1) the optical fiber in which the high reflection fiber Bragg grating FBG-HR is formed at one end of the amplification fiber AF is fused (2) The optical fiber having the low reflection fiber Bragg grating FBG-LR formed on the other end of the amplification fiber AF is fused, and (3) the amplification of the end of the low reflection fiber Bragg grating FBG-LR The method further includes the step of fusing an optical fiber having a slant fiber Bragg grating SFBG formed at the end opposite to the fiber AF.
- the manufacturing method S3 of the modification has the same effect as the manufacturing method S3 shown in FIG. Further, according to the manufacturing method S3 of the modification, it is possible to manufacture the fiber laser system FLS in which the temperature rise that may occur during actual use is suppressed.
- the manufacturing method S3 including the heating condition setting method S1 is an optical fiber doped with ytterbium (for example, an amplification fiber).
- the present invention can be applied to the formation of a fiber Bragg grating or slant fiber Bragg grating in AF), or to the formation of a fiber Bragg grating or slant fiber Bragg grating in an optical fiber not doped with ytterbium. .
- Three fiber Bragg gratings (high reflection fiber Bragg grating FBG-HR, low for the amplification fiber AF that is a single optical fiber) Form reflective fiber Bragg gratings FBG-LR and slant fiber Bragg gratings SFBG) (see FIG. 8) or (2) form three fiber Bragg gratings respectively for each of three separate optical fibers Depending on the heating conditions (T, t) set for each of the three fiber Bragg gratings, for example (see FIG. 9) can be determined as appropriate.
- At least one of the high reflection fiber Bragg grating FBG-HR and the low reflection fiber Bragg grating FBG-LR among the three fiber Bragg gratings is formed in the amplification fiber, and the other A configuration in which the fiber Bragg gratings of (1) are formed in separate optical fibers may also be employed.
- the heating condition setting method includes a fiber Bragg grating (high reflection fiber Bragg grating FBG-HR, low reflection fiber Bragg grating FBG-LR, and slant fiber Bragg grating A method of setting heating conditions when thermally aging a grating (SFBG), the temperature coefficient based on the correspondence relationship (Ed) between the temperature coefficient ⁇ of the fiber Bragg grating and the relaxation energy Ed of the fiber Bragg grating.
- the step of setting the (S12, S22) includes, characterized in that.
- the relaxation energy Ed has predetermined values Ed1, Ed2, ..., Edn (n is a natural number of 2 or more) It is preferable that the method further includes the step (S10) of deriving the correspondence relationship ⁇ (Ed) from the temperature coefficients ⁇ 1, ⁇ 2,.
- the correspondence relationship ⁇ (Ed) is a linear correspondence relationship in at least a part of the region.
- the heating condition setting method (heating condition setting method S2) according to an embodiment of the present invention is the correspondence NCC between the normalized coupling constant NCC of the fiber Bragg grating and the relaxation energy Ed of the fiber Bragg grating.
- a step (S21) of specifying the lower limit value Edmin 'of the relaxation energy Ed where the normalized coupling constant NCC is equal to or less than the desired upper limit value NCCmax based on (Ed) the step of setting the heating condition S22) sets a heating condition at the time of thermal aging of the fiber Bragg grating such that the relaxation energy Ed is equal to or greater than Edmax, where Edmax is the larger of the lower limit Edmin and the lower limit Edmin '. Is preferred.
- a fiber Bragg grating according to an embodiment of the present invention (1, 1A, 1B, 1C, and a high reflection fiber Bragg grating FBG-HR and a low reflection fiber Bragg grating FBG-LR are formed in the vicinity of both end portions.
- the manufacturing method of the amplification fiber AF is set in the setting step of setting the heating condition when heat aging the fiber Bragg grating according to the setting method (heating condition setting method S1, S2), and the setting step Thermal aging step (S33) of thermally aging the fiber Bragg grating to satisfy the heating condition.
- a method (S3) of manufacturing a fiber laser system (FLS) is to make the excitation light source (PSj), the amplification fiber (AF), and the amplification fiber function as a resonator 2
- FLUi fiber laser unit
- a method of manufacturing a single fiber laser system comprising the steps of manufacturing each of the two fiber Bragg gratings using the method of manufacturing a fiber Bragg grating according to an embodiment of the present invention. It features.
- the fiber laser unit (FLUi) is configured to generate the stimulated Raman scattering light corresponding to the laser light generated by the amplification fiber (AF).
- the method further includes the step of manufacturing the slant fiber Bragg grating using the method of manufacturing the fiber Bragg grating according to the embodiment of the present invention, further comprising a slant fiber Bragg grating (SFBG) which preferentially loses the laser light. Is preferred.
- SFBG slant fiber Bragg grating
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Abstract
Description
ファイバブラッググレーティングの長期信頼性を示す指標のひとつに温度係数γ[℃/W]がある。温度係数γは、ファイバブラッググレーティングの温度τ[℃]を、ファイバブラッググレーティングを導波する光のパワーP[W]の関数τ(P)と見做したときの傾きdτ/dPとして定義される量である。温度係数γが大きいファイバブラッググレーティングは、実使用時に高温になり易く、長期信頼性が低い。一方、温度係数γが小さいファイバブラッググレーティングは、実使用時に高温になり難く、長期信頼性が高い。
本発明の第1の実施形態に係る加熱条件設定方法S1について、図1を参照して説明する。図1は、加熱条件設定方法S1の流れを示すフローチャートである。加熱条件設定方法S1は、ファイバブラッググレーティングの熱エージングの加熱条件を設定する方法であり、以下に説明する工程S10~S12を含む。なお、本実施形態においては、離脱速度ν0は既知であるものと仮定する。離脱速度ν0が未知である場合には、第2の実施形態として後述するように、加熱条件設定方法S2に含まれる工程S20を実施することによって、離脱速度ν0を定めてから、以下に説明する工程S21、工程S10~S11、及び工程S22を実施すればよい。
加熱条件設定方法S1の適用例について、表1及び図2を参照して説明する。
本発明の第2の実施形態に係る加熱条件設定方法S2について、図3を参照して説明する。図3は、加熱条件設定方法S2の流れを示すフローチャートである。加熱条件設定方法S2は、加熱条件設定方法S1において、工程S12を省略すると共に、工程S10の前に工程S20~S21を追加し、工程S11の後に工程S22を追加したものである。したがって、加熱条件設定方法S2においては、工程S20、工程S21、工程S10、工程S11、工程S22がこの順に実施される。
加熱条件設定方法S2の適用例について、図4、図5、及び表2を参照して説明する。本適用例は、上記の工程20において、FBG1、FBG2、及びFBG3を、それぞれ、T1=250℃、T2=300℃、及びT3=350℃で熱エージングした場合の適用例である。
本発明の第3の実施形態に係るファイバレーザシステムの製造方法S3について、図7~図9を参照して説明する。図7は、製造方法S3の流れを示すフローチャートである。図8は、製造方法S3の適用対象となり得るファイバレーザシステムの第1の典型例であるファイバレーザシステムFLSの構成を示す構成図である。図9は、製造方法S3の適用対象となり得るファイバレーザシステムの第2の典型例であるファイバレーザシステムFLSの構成を示す構成図である。
第1の典型例のファイバレーザシステムFLSは、加工対象物であるワークWを加工するためのレーザ装置であり、図8に示すように、n個のファイバレーザユニットFLU1~FLUn、n個のレーザデリバリファイバLDF1~LDFn、出力コンバイナOC、出力デリバリファイバODF、及び出力ヘッドOHを備えている。ファイバレーザユニットFLU1~FLUnとレーザデリバリファイバLDF1~LDFnとは、互いに一対一に対応する。ここで、nは、1以上の任意の自然数であり、ファイバレーザユニットFLU1~FLUn及びレーザデリバリファイバLDF1~LDFnの個数を表す。なお、図5においては、n=7の場合のファイバレーザシステムFLSの構成例を示している。また、出力コンバイナOCは、n個の入力ポートと1つの出力ポートを備えている。出力コンバイナOCは、各入力ポートに入力されたn個のレーザ光を1つのレーザ光に合波し、合波したレーザ光を出力ポートから出力する。
ファイバレーザシステムFLSが備えるファイバレーザユニットFLU1の構成について、引き続き図8を参照して説明する。なお、ファイバレーザユニットFLU2~FLUnも、ファイバレーザユニットFLU1と同様に構成されている。
図7に示した製造方法S3は、図8に示したファイバレーザシステムFLSを製造する製造方法であり、以下に説明する工程S31~S33と、工程S32と工程S33との間に実施される加熱条件設定方法S1とを含む。なお、製造方法S3に含まれる加熱条件設定方法S1は、図1に示した加熱条件設定方法S1と同じであるため、本実施形態では、その説明を省略する。
図9に示すように、第2の典型例のファイバレーザシステムFLSは、第1の典型例のファイバレーザシステムFLS(図8参照)が備えているn個のファイバレーザユニットFLUiの代わりに、1個のファイバレーザユニットFLU1を備えている。第2の典型例のファイバレーザシステムFLSが備えるファイバレーザユニットFLU1は、第1の典型例のファイバレーザシステムFLSが備えているファイバレーザユニットFLU1と同様の構成を有する。ただし、ファイバレーザシステムFLSが備えるファイバレーザユニットFLU1は、ファイバレーザシステムFLSが備えているファイバレーザユニットFLU1と比較して、高反射ファイバブラッググレーティングFBG-HR、低反射ファイバブラッググレーティングFBG-LR、及びスラントファイバブラッググレーティングSFBGの各々が増幅用ファイバAFに直接形成されているのではなく、それぞれ、増幅用ファイバAFとは別個の光ファイバに形成されている点が異なる。
図9に示したファイバレーザシステムFLSは、図7に示した製造方法S3の一部を変形した変形例を用いて製造することができる。ここでは、変形例の製造方法S3において図7に示した製造方法S3から変更した点についてのみ説明する。
本発明の一実施形態に係る加熱条件の設定方法(加熱条件設定方法S1,S2)は、ファイバブラッググレーティング(高反射ファイバブラッググレーティングFBG-HR、低反射ファイバブラッググレーティングFBG-LR、及びスラントファイバブラッググレーティングSFBG)を熱エージングする際の加熱条件の設定方法であって、上記ファイバブラッググレーティングの温度係数γと上記ファイバブラッググレーティングの緩和エネルギーEdとの間の対応関係γ(Ed)に基づき、温度係数γが所望の上限値γmax以下となる、緩和エネルギーEdの下限値Edminを特定する工程(S11)と、緩和エネルギーEdが下限値Edmin以上になるように、上記ファイバブラッググレーティングを熱エージングする際の加熱条件(T,t)を設定する工程(S12,S22)と、を含んでいる、ことを特徴とする。
本発明は、上述した各実施形態に限定されるものでなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。
S10 対応関係γ(Ed)を導出する工程
S11 緩和エネルギーEdの下限値Edminを特定する工程
S12 加熱条件(T,t)を設定する工程
S2 加熱条件設定方法
S21 対応関係NCC(Ed)を導出する工程
S22 緩和エネルギーEdの下限値Edmin’を特定する工程
S23 加熱条件(T,t)を設定する工程
S3 製造方法
S31 ファイバブラッググレーティングを形成する工程
S32 スラントファイバブラッググレーティングを形成する工程
S33 ファイバブラッググレーティングを熱エージングする工程
Claims (7)
- ファイバブラッググレーティングを熱エージングする際の加熱条件の設定方法であって、
上記ファイバブラッググレーティングの温度係数γと上記ファイバブラッググレーティングの緩和エネルギーEdとの間の対応関係γ(Ed)に基づき、温度係数γが所望の上限値γmax以下となる、緩和エネルギーEdの下限値Edminを特定する工程と、
緩和エネルギーEdが下限値Edmin以上になるように、上記ファイバブラッググレーティングを熱エージングする際の加熱条件を設定する工程と、を含んでいる、
ことを特徴とする加熱条件の設定方法。 - 緩和エネルギーEdが予め定められた値Ed1,Ed2,…,Edn(nは2以上の自然数)になるまで熱エージングしたファイバブラッググレーティングの温度係数γ1,γ2,…,γnから、対応関係γ(Ed)を導出する工程を更に含んでいる、
ことを特徴とする請求項1に記載の加熱条件の設定方法。 - 対応関係γ(Ed)は、少なくとも一部の領域において線形な対応関係である、
ことを特徴とする請求項1又は2に記載の加熱条件の設定方法。 - 上記ファイバブラッググレーティングの規格化結合定数NCCと上記ファイバブラッググレーティングの緩和エネルギーEdとの間の対応関係NCC(Ed)に基づき、規格化結合定数NCCが所望の上限値NCCmax以下となる、緩和エネルギーEdの下限値Edmin’を特定する工程を更に含んでおり、
上記加熱条件を設定する工程は、上記下限値Edmin及び上記下限値Edmin’のうち大きい方をEdmaxとして、上記緩和エネルギーEdがEdmax以上になるように、上記ファイバブラッググレーティングを熱エージングする際の加熱条件を設定する工程である、
ことを特徴とする請求項1~3の何れか1項に記載の加熱条件の設定方法。 - 請求項1~4の何れか1項に記載の加熱条件の設定方法に従って、ファイバブラッググレーティングを熱エージングする際の加熱条件を設定する設定工程と、
上記設定工程にて設定された加熱条件を満たすように上記ファイバブラッググレーティングを熱エージングする熱エージング工程と、を含んでいる、
ことを特徴とするファイバブラッググレーティングの製造方法。 - 励起光源と、増幅用ファイバと、上記増幅用ファイバを共振器として機能させる2つのファイバブラッググレーティングであって、それぞれの反射率が互いに異なる2つのファイバブラッググレーティングと、を含むファイバレーザユニットを少なくとも1台備えているファイバレーザシステムの製造方法であって、
請求項5に記載のファイバブラッググレーティングの製造方法を用いて上記2つのファイバブラッググレーティングの各々を製造する工程を含んでいる、
ことを特徴とするファイバレーザシステムの製造方法。 - 上記ファイバレーザユニットは、増幅用ファイバにより生成されたレーザ光の波長に対応する波長を有する誘導ラマン散乱光を上記レーザ光よりも優先的に損失させるスラントファイバブラッググレーティングを更に含み、
上記ファイバブラッググレーティングの製造方法を用いて上記スラントファイバブラッググレーティングを製造する工程を更に含んでいる、
ことを特徴とする請求項6に記載のファイバレーザシステムの製造方法。
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US16/643,144 US20200348464A1 (en) | 2017-08-31 | 2018-07-31 | Method for setting heating condition, method for manufacturing fiber bragg grating, and method for manufacturing fiber laser system |
EP18850940.0A EP3677936A1 (en) | 2017-08-31 | 2018-07-31 | Method for setting heating condition, method for manufacturing fiber bragg grating, and method for manufacturing fiber laser system |
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US20040161195A1 (en) * | 2003-02-14 | 2004-08-19 | Teraxion Inc. | Method for manufacturing a FBG having improved performances and an annealing-trimming apparatus for making the same |
JP2004325796A (ja) * | 2003-04-24 | 2004-11-18 | Sumitomo Electric Ind Ltd | 光導波路型回折格子素子製造方法 |
JP5298238B2 (ja) | 2010-03-30 | 2013-09-25 | 株式会社フジクラ | 光ファイバグレーティングの製造方法、光ファイバグレーティング及びファイバレーザ |
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US20040161195A1 (en) * | 2003-02-14 | 2004-08-19 | Teraxion Inc. | Method for manufacturing a FBG having improved performances and an annealing-trimming apparatus for making the same |
JP2004325796A (ja) * | 2003-04-24 | 2004-11-18 | Sumitomo Electric Ind Ltd | 光導波路型回折格子素子製造方法 |
JP5298238B2 (ja) | 2010-03-30 | 2013-09-25 | 株式会社フジクラ | 光ファイバグレーティングの製造方法、光ファイバグレーティング及びファイバレーザ |
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